Signal-type dependent real-time fax relay

ABSTRACT

In order to enable V.34 fax relay communications over IP (“FoIP”) without increasing a gateway complexity, the gateway relays all types of fax control signals in demodulated form and transfers fax image type signals either as demodulated or as PCM encoded signal, based on a predetermined condition. The PCM data type is added to FoIP protocol to allow transferring PCM encoded fax image signals without exiting from FoIP mode of operation until the completion of a fax call. During a FoIP call, the communicating gateway determines whether the input fax signal is a ‘fax control signal’ or a ‘fax image’ type signal. If the gateway determines that the input signal is a fax control signal or supported fax image signal, it handles it in a traditional fax relay manner. However, if the gateway determines that the input fax image type signal cannot be demodulated, it outputs the fax signal to the IP network as PCM encoded signal and without performing demodulation

FIELD OF THE INVENTION

The present invention relates generally to the field of facsimilecommunications. More specifically, the present invention relates to thefield of real-time fax relay generally called fax over IP (“FoIP”)communications, and even more specifically, to a signal type dependentreal-time fax relay used in connection with FoIP systems

BACKGROUND

The development of the Internet and other similar distributed datacommunication networks (i.e., Internet Protocol (“IP”) based networks,or, simply, ‘IP networks’) has facilitated a growth in the number ofpeople using IP-based networks to exchange various types of information,such as voice, fax and modem calls. The key method supporting fax callsover packet networks is the fax over IP (“FoIP”).

Fax relay is considered a reliable method for carrying out ‘end-to-end’fax communications over IP networks. The communication protocol of FoIPsystems is described in ITU-T Recommendation T.38 (“Procedures forreal-time Group 3 facsimile communication over IP networks”) Roughly,ITU-T T.38 is a set of rules defining the FoIP call establishment andthe packet format for transferring different signals of regular G3 and V34 half-duplex (“HDX”) fax calls. The other fax relay protocol isdefined in the Voice over Frame Relay Implementation Agreement FRF 11but it has a limited use in comparison to T.38.

Traditionally, fax machines were, and still are, designed to make faxcalls via a public switched telephone network (“PSTN”). The way in whichsuch fax calls are managed and the way they traverse the PSTNinfrastructure is defined in the ITU-T Recommendation T.30 (“Proceduresfor document facsimile transmission in general switched telephonenetworks”). Briefly, fax machines employ modulation schemes for allowingsuch traversals. However, for enabling FoIP calls, the signal output bya fax machine must be translated into a bit stream suitable fortransmission via an IP network. The translation is performed by acorresponding media gateway (hereinafter “gateway”) that is connected onone hand to the fax terminal or PSTN, and, on the other hand, to the IPnetwork. Such media gateways typically include a ‘fax relay’, speechcoder and voice band data (“VDB”) paths for enabling fax calls, verbaland modem communication, respectively, as schematically shown in FIG. 1.

Traditionally, voice-over-IP (‘VoIP’) gateways process input and outputvoice band signals at 8 kHz sampling rate. Gateways exchange the signalswith analog devices via interface circuits. Higher sampling rates areallowed as well However, for pulse code modulation (“PCM”) basedtransfer over IP, which is based on bit rates up to 64 kbps(kilo-bits-per-second), the signals should be sampled at a rate of 8kHz. Typically, the input samples represent a sine waveform (carrier)signal modulated by a digital bit stream according to a standardmodulation scheme. The modulating bit stream may contain some usefulinformation such as fax capabilities, commands, responses, image bitmap, transferred binary file, mixed raster content, etc

A purpose of fax gateways is to deliver all or most of the signalsend-to-end between two communicating fax machines by a way that thefaxes are able to complete a fax call/session without error alarms andsuch that an answering fax machine may receive analog signals from agateway and extract a binary information transferred to it by the‘In-Message’ procedure, and interpret it as intended by the originatingfax.

Typically, fax relay gateways detect, demodulate and re-modulate alltypes of fax signals from the beginning till the end of a fax call.Usually, if the gateway is unable to relay at least some fax signalsthen it employs the VBD method to transfer a complete call over IP. Itis noted that by using the wording ‘VBD method’ and ‘fax relay’ it isalso meant to include the use of corresponding software tools, hardware,algorithms and applications as required for operating these circuitries.

By ‘VBD’ is meant method according to which modem's signals aretransported over IP networks using a codec that passes voice band datamodulated signals with minimum distortion. Exemplary VBD codecs are theG.711 A-law and G 711μ-law codecs, which are commonly utilized by ITU-TV.150.1 (“Procedures for the end-to-end connection of V-series DCEs overan IP network”) and ITU-T V.152 (“Procedures for supporting Voice-BandData over IP Networks”) standards PCM encoders of the G.711 type outputbit streams at the rate 64 kbps, whereas PCM encoders of the G.726 typeoutput bit streams at a rate of up to 40 kbps.

Typical FoIP media gateways, readily available on the market, wereprimarily designed to cope with (regular) group 3 (“G3”) fax machines,which are capable of producing HDX fax image data streams at a bit-rateless than or equal to 14 4 kbps, and exchanging HDX fax's controlsignals at a rate of 300 bps. After being received by a gateway, thesesignals are handled by the fax relay. The fax signal translationperformed in the gateway involves demodulation of the incoming sampledsignal by a fax relay receiver, packetization of the demodulated dataaccording to a fax relay protocol (‘FRP’), and transmittal of the FRPpackets to the IP network. A receiving gateway includes a fax relaytransmitter, the task of which is to re-modulate the FRP packets,received from the packet network, according to modulation schemes thatare defined for G3-type faxes in the ITU-T Recommendation T.30

Currently, there exist V 34-type fax machines that are known to thoseskilled in the art also as “super-G3” fax machines, which have a signalflow and modulation schemes that are more advanced in comparison tothose of regular G3 fax machines. For example, a super-G3 fax machinetransfers HDX fax images at a bit-rate as high as 33 6 kbps (vs 14.4kbps in G3 fax machines) and exchange different types of fax controlsignals full duplex at bit-rates of 300, 600 and 1200 (2400) bps. Fullsupport of V.34 fax relay as defined by T.38 Rec. is highly problematicdue to considerable computational resources that are required, on thereceiving/transmitting gateway side, for processing V.34 fax images andtraining equalizer signals.

Traditional gateways avoid the latter obstacle by using the relativelylow-complex VBD method. They do so by switching to VBD ‘mode ofoperation’, handling and transferring (i.e., over the IP network) theincoming V.34 type signals as if they were voice band modem signals;i.e., without demodulation. However, as far as operating under real IPnetwork conditions, the latter solution is very problematic shorthandand unsatisfying; that is, IP networks have variable packet latency,multi-node packet processing and bandwidth restrictions. Morespecifically, the problems associated with the latter solution are thefollowing:

i) Data streams exchanged by gateways are required to be full duplex atbit-rates of 64 kbps in order to allow communications at fax rates above7.2 kbps;

ii) The ‘VBD path’ (i.e., in a gateway) is highly sensitive to residualechoes and imperfection of echo canceling process, which tend to cause‘fallbacks’ in bit-rates, inaccurate reconstruction of the original faximages, and fax calls failures;

iii) The traditional solution involving usage of VBD is sensitive topacket latency. Long constant delays of packets in the IP network maycause signal collisions at the destination fax machine, and failure orabortion of fax sessions;

iv) The ‘VBD path’ is highly sensitive to packet jitter (variable delay)in the network. An attempt to extend the input queue buffers for solvingthis problem would result in large constant delays, possible collisionsof fax signals, and ‘timeout’ related disconnections, and

v) The ‘VBD path’ solution is highly sensitive to packet loss.

Therefore, as far as super-G3 fax terminal equipments are concerned,traditional gateways provide a solution that is far from being adequate.

SUMMARY OF THE INVENTION

In general, the present invention is characterized by not utilizing thecommonly known VBD method for delivering fax calls but, rather, byemploying a novel type of ‘fax relay’ for all available types of faxsignals (i.e., control and image relating signals) because a fax relayis more reliable in comparison to the VBD method.

As part of the present invention, a method of delivering fax callsbetween gateways over an IP network is provided, according to which adistinction is made between two types of fax signals, the first typebeing generally associated with ‘fax control signals’, and the secondbeing generally associated with ‘fax image signals’, wherein gatewaysrelay all types of fax control signals in demodulated form andconditionally transfer fax image type signals either as a demodulatedsignal or as a PCM encoded signal, based on a predetermined condition.

In some embodiments of the present invention, the predeterminedcondition of relaying fax image signals in demodulated form may relate,e.g., to the availability of computational resources in the gatewayrequired for performing the demodulation process, and/or to whether thegateways involved both support the modulation scheme used by the faxmachines. Of course, other considerations may be taken into account,whether cumulatively or uniquely, when employing the predefineddemodulation condition.

More specifically, if the gateway does not support a modulation schemethat is currently utilized by a fax machine, or the gateway does nothave enough computational resources for performing demodulation, thenthe gateway may forward the signal in question to the IP networkessentially ‘as is’, by using minimum-distortion PCM encoder withoutdeparting from the fax relay mode of operation. In turn, when thegateway receives an FRP stream containing PCM-type data from the IPnetwork, it must be able (in addition to its ‘conventionalre-modulation’ capability) to decode PCM-type data and transmit theoutput signal to a connected fax machine in conformity to T.30requirements.

As part of the present invention, a method is disclosed for processingin real-time an outgoing fax over IP (“FoIP”) signal by a gateway,comprising:

a) Receiving an incoming fax signal and, based on its signalcharacteristics, associating it either with a first type of signals(e.g., if it is a fax control signal) or with a second type of signals(i.e., If it is a fax image signal),

b) Demodulating the fax signal if it is associated with the first typeof signals (and, therefore must be de-modulated) or if it is associatedwith the second type of signals and it is decided that it is within thegateway's capacity to demodulate the fax signal; and outputting theresultant FRP packetized data to the IP network; otherwise,

c) PCM-encoding the fax signal and outputting the resultant FRP-PCMpacketized data to the IP network.

In some embodiments of the present invention, an incoming fax signal isassociated with the first type of signals and relayed (unconditionally)if it belongs to the group signals consisting of {Answer fax toneincluding V.8 modified answer tone; V.21 (FSK, 300 bps), V.34 INFO(DPSK, 600 bps); V.34 Control Channel (QAM, 1200 bps or 2400 bps)}Calling fax signals that precede an answer tone (e.g., CNG and V 8 Clsignals) may be conveniently transferred in the form of compressed voicesignals or in a form of fax events that are relayed using VoIP or FoIPtechnique.

In some embodiments of the present invention, an incoming fax signalbelonging to the group consisting of {V.27 (Phases B and C); V.29(Phases B and C), V 17/V 33 (Phases B and C); V 34 Line probe (Phase B);V.34 Primary channel equalizer training (Phase B); V 34 Primary channel(Phase C)}, is associated with the second type of signals and isdemodulated if there are enough computational resources fordemodulation, otherwise it is PCM-encoded before being forwarded to thepacket network

As part of the present invention a method is disclosed for processing inreal-time a fax over IP (“FoIP”) signal received by a gateway,comprising.

a) Determining whether the received fax signal is FRP-type data orFRP-PCM type data (i.e., depending on the type of signal that wasoriginally transmitted to the gateway by a remote gateway;

b) Re-modulating the incoming fax signal if it is determined to beFRP-type data, and forwarding the resultant signal (in the form ofsamples) to an intended recipient (normally a fax machine); or

c) PCM-decoding the incoming fax signal if it is determined to beFRP-PCM type data, and forwarding the resultant signal (in the form ofsamples) to the intended recipient.

As part of the present invention, the determination how to process(i.e., performing demodulation or PCM-encoding) the incoming fax signalmay be made by judging, such as by a ‘state machine’, a currently, andhistorically based on previously detected or demodulated fax signals andreceived FRP data from the IP network. The judging may also be based onthe gateway capabilities and on the estimation of resources availablefor performing demodulation.

The present invention also discloses a ‘fax relay state machine’ forallowing FoIP communication between gateways delivering fax calls overan IP network The fax relay state-machine is operable to.

a) Be configured with a set of rules associated with the potentialemployment of any available fax modulation schemes, and by a temporaryset of rules intended for supporting fax modulation schemes that may bepotentially used in a current fax call while taking into accountavailable computational resources;

b) Evaluate current and historic input fax signals based on the fax andFRP data responses returned from a remote gateway;

c) Judge, based on the evaluation, whether the input fax signal can bedemodulated and, if the input digital signal can be demodulated, then toinvoke a corresponding fax receiver and to forward the resultant FRPdata to the IP network;

d) Invoke PCM encoding and to forward the resultant FRP-PCM type data tothe IP network without performing any demodulation;

e) Buffer the FRP-type data stream arriving from the IP network, and to

f) Invoke a fax transmitter or a PCM-decoder in a way that the outputfax signals would conform to the ITU-T T 30 Recommendation

In one aspect, the fax relay resides within the gateway. In anotheraspect, the fax relay is external to the gateway and in communicationwith it.

As part of the present invention, a gateway is also disclosed, whichincludes the novel fax relay.

In some preferred embodiments of the present invention, the gatewayfurther includes also a speech coder and a VBD path.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specificationThe invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 (prior art) is a block diagram showing an exemplary conventionalgateway used for delivering fax calls over an IP network;

FIG. 2 is a block diagram showing signals flow in an exemplary fax relaywhile in ‘originate’ mode of operation according to some preferredembodiments of the present invention; and

FIG. 3 is a block diagram showing signals flow in an exemplary fax relaywhile in ‘answer’ mode of operation according to some preferredembodiments of the present invention.

By ‘originate’ or ‘answer’ mode is meant herein to the mode of operationof a fax relay unit when operating at the side of a facsimile terminalthat sends or receives fax image signals to, or from, a connectedfacsimile terminal, respectively.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, components and circuitshave not been described in detail so as not to obscure the presentinvention

Unless specifically stated otherwise, as apparent from the followingdiscussions, it is appreciated that throughout the specificationdiscussions utilizing terms such as “processing”, “computing”,“calculating”, “determining”, or the like, refer to the action and/orprocesses of a computer or computing system, or similar electroniccomputing device, that manipulate and/or transform data represented asphysical, such as electronic, quantities within the computing system'sregisters and/or memories into other data similarly represented asphysical quantities within the computing system's memories, registers orother such information storage, transmission or display devices.

Embodiments of the present invention may include apparatuses forperforming the operations herein This apparatus may be speciallyconstructed for the desired purposes, or it may comprise a generalpurpose computer selectively activated or reconfigured by a computerprogram stored in the computer. Such a computer program may be stored ina computer readable storage medium, such as, but is not limited to, anytype of disk including floppy disks, optical disks, CD-ROMs,magnetic-optical disks, read-only memories (ROMs), random accessmemories (RAMs) electrically programmable read-only memories (EPROMs),electrically erasable and programmable read only memories (EEPROMs),magnetic or optical cards, or any other type of media suitable forstoring electronic instructions, and capable of being coupled to acomputer system bus.

The processes and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct a more specializedapparatus to perform the desired method. The desired structure for avariety of these systems will appear from the description below. Inaddition, embodiments of the present invention are not described withreference to any particular programming language. It will be appreciatedthat a variety of programming languages may be used to implement theteachings of the inventions as described herein.

In particular, the method disclosed in the present invention is notlimited to a specific type of a packet (or IP) network, communicationprotocol or standard for relaying demodulated fax data.

In the following description, packets encoded according to a Fax RelayProtocol (“FRP”), such as T 38 and FRF.11, are herein referred to as“FRP” packets. In addition, the present invention is not intended to belimited to a specific facsimile's modulation scheme described in the ofITU-T T.30 Recommendation. For example, the method disclosed herein maybe used for relaying also non-standard fax calls.

As known in the art of telecommunications, in cases where voicetransmissions are involved, the original voice signal is first digitizedby an external analog to digital (“A/D”) converter (i.e., CODEC). Atypical CODEC samples the analog Tel/Fax/Modem signal at sampling rate 8kHz and outputs the digitized signal as series of linear 16-bit samplesor 8-bit compressed PCM A-law or μ-law bytes

The term ‘fax over IP’ (FoIP) refers generally to facsimilecommunication over IP network by using the fax relay protocol defined in“ITU-T Recommendation T.38”. However, it is noted that the presentinvention can be applied, mutatis mutandis, essentially to any other faxrelay protocol/standard and other packet networks.

As described hereinbefore, an input fax signal may belong either to afirst or to a second type of signals In general, the first type ofsignals (i.e, fax control signals) may include, inter alia, T 30 Phase Atype Tone signals, V.21-modulation based signals and V.34 ‘INFO’ and V34 ‘Control Channel’ signals Signals belonging to the first group arecharacterized by being relatively ‘simple’ signals, that is, they aresimple in the sense that their processing does not require muchcomputational resources, and therefore, in accordance with theprinciples of the present invention, signals belonging to the first typeare conventionally relayed by gateways over IP network; that is, thegateways detect them, demodulate and forward the resultantfax-relay-protocol (FRP) data to the IP network. Upon receipt of the FRPdata, the gateways generate or re-modulate corresponding fax signals andforward them to intended recipient (normally a fax machine).

The second type of signals (i.e, ‘fax image signals’) may include, interalia, signals relating to the fax ‘In-Message’ procedure itself (i.e.,T.30 Phase C signals), and to T 30 Phase B type ‘pre-message’ signalssuch as ‘training check frame’ (“TCF”), V 34 ‘line probe’ signals andV.34 ‘Primary Channel’ equalizer training (“TRN”) signals.

Signals belonging to the second type of signals may be conditionallyrelayed in demodulated form or are said to be ‘transparently’transferred over IP between gateways by using PCM encoding, FRP format,and PCM decoding.

A determination as to how and when to process (i e, performingdemodulation or PCM-encoding) the incoming fax signal may be made byjudging, such as by a ‘state machine’, a currently, and historicallybased on previously detected or demodulated fax signals and received FRPdata from the IP network. The judging may also be based on the gatewaycapabilities and on the estimation of resources available for performingdemodulation.

Some judgment is traditionally performed by various types of gatewaysfor anticipating a current step in a specific fax communication/session.This judgment is essential because a gateway must ‘know’ in advance whatthe current step in a specific fax communication is going to be, inorder to allow it to timely ‘prepare’ itself for a currently incomingsignal; that is, by enabling circuitries relevant to the current signaland disabling, or muting other irrelevant circuitries, and by employingcorresponding signal processing within the gateway. However, accordingto the present invention, the results of the judgment are somewhatdifferent than the traditional one, as disclosed herein.

For correct functioning of the signal-type dependent fax relay beingdisclosed in the present invention, the PCM-based, and possibly someother modulation type(s), would be added into FoIP protocolproprietarily by a gateway's vendor or officially via ITU-T or by anyother suitable forum.

At the stage of a FoIP call setup, the gateway compliant with theprinciples disclosed by the present invention negotiates the ‘FRP-PCMcapability’ with the other FoIP capabilities The FRP-PCM mode ofoperation must be disabled if it is not confirmed by a remote gateway.In the latter case, the fax calls, for example V 34 fax calls, thatcannot be relayed by the gateway may be transferred using a regular VBDmode of operation.

The invention considers the PCM scheme used during fax relay sessions asan integral part of FoIP protocol together with the other modulationschemes of fax signals. The PCM-based transfer of fax image signals(i.e., signals relating to the second type of fax signals) differs fromVBD transfer, the differences therebetween being the following

PCM stream is packetized in primary IP fax packets according to FRP(FoIP) rules but not according to RTP rules applied to VBD andcompressed voice streams, while an upper level packetizing of primaryfax packets may include RTP and other IP formats as well. For example,T.38 may be encapsulated in RTP;

2) Occasionally, a gateway may decide to switch from PCM mode ofoperation into demodulation mode of operation, and vice versa, toaccommodate to actual signal type that depends on the current stage in afax session/call being currently handled;

3) A gateway stays in FoIP mode of operation throughout the entire faxcall; namely, no transitions take place between the “Audio”, “VBD” and“FoIP” states/modes of operation during a given fax call. Therefore,PCM-type data streams are substantially insensitive to disrupts (i e,they are not distorted) and to temporally misplaced silence ‘gaps’ thatmay occur during transitions/switching between the states;

4) gateway transferring a FRP-PCM type data stream may, at the sametime, process the fax control signals (i.e., signals belonging to thefirst type of signals) relayed by using FoIP method

Turning now to FIG. 1, the gateway 100 may receive, at times, Telephone,Fax or Modem (‘Tel/Fax/Modem’) analog signals sampled at 8 kHz fromserial port interface, or TDM port, 101. If in compressed form, theinput samples are expanded by the gateway into linear 16-bit samples(102). Synchronously with receiving input samples, the gateway 100transmits output samples to the serial or TDM port 101. If required, theoutput samples are compressed by gateway 100 before being transmitted.

The output samples transmitted to the analog signal interface 101 areutilized by echo canceller 103 as a reference to filter the incomingsignal, whereby to obtain echoless signal 104. The voice/fax/data calldiscriminator 105 constantly monitors the echo-free input signal 104. Ifdiscriminator 105 detects a voice signal, the incoming samples areforwarded to speech encoder 106. If it detects a fax signal, the samplesare forwarded to fax relay 108 for demodulation. In case of a modemsignal being detected by discriminator 105, the input samples areforwarded to VBD encoder 107. As described hereinbefore in connectionwith traditional operation of gateways, if the input signal 102originates from a super-G3 (i.e., V.34) fax machine, the gateway 100routes the samples via VDB path 107 as if they were originated by amodem call. The consequences resulting from this solution were discussedhereinabove,

Depending on the path of signal processing, gateway 100 packetizes theoutput bit-streams according to the real-time transport protocol RTP(109) or fax relay protocol T.38 (110), and transfers the packets (111)to the network packet interface (112), which forwards it, possibly aftersome modifications, to the IP network (not shown) The bit-stream passingthrough interface 112 may relate, at times, either to the compressedvoice or to PCM encoded modem or to the demodulated fax signals.

No further description will be given hereinafter in respect of theblocks shown in FIG. 1, because their functionality is well known tothose skilled in the field of voice over IP technologies.

Turning to FIG. 2 and FIG. 3, they show block diagrams of a fax relayhandling an originating (200) and answer (300) fax call, respectively,in accordance with the present invention. In respect of fax controlsignals, gateways 200 and 300 perform a similar bi-directionalcommunications processing. Namely, each of the gateways 200 and 300 mayboth receive and transmit fax control signals from/to a connected faxmachine. In respect of fax image signals propagating only in onedirection, gateway 200 only receives this type of signals from anoriginating fax machine, while gateway 300 only transmits fax imagesignals to an answering fax machine

Fax relay gateway 200/300 receives the sampled input fax signal 102,filtered by the echo canceller 103. The fax relay state machine ofgateways 200/300 (not shown) determines how the input signal should beprocessed. In one aspect, the latter determination is made according tothe input signal analysis performed by signal detector 201/301, whichmonitors the echo-free input samples 104. In another aspect, thedetermination is based on monitoring fax packets received from the IPnetwork. As part of the analysis process, the state machine considersthe history of previous signal sequences that were received from andtransmitted to a connected fax machine. The decision about the type of acurrently received, or handled, signal (i.e., fax control or fax image)is made per every signal. The decision as to how to process fax imagesignals is taken by the state machine one time per fax call, anddepending on the type of the fax call (i.e., regular G3 or V.34 faxcall), and on the amount of computational resources required (andavailable) for processing a current call.

If the state machine determines that signal 104 relates to T.30 Controltype signals, it causes signal 104 to be routed to the ‘T.30 Controlpath’, where signal 104 is first processed by T.30 Control receiver202/302.

Receivers 202 and 302 are advantageously designed for demodulating faxcontrol signals According to the T.30 standard dated 07/2003, such faxcontrol signals are the following. V 21 (frequency shift keying—FSK, 300bps), V.34 INFO (differential phase shift keying—DPSK, 600 bps) and V.34Control Channel (quadrature amplitude modulation—QAM, 1200 bps or 2400bps). Receiver 202/302 operates in a frequency spectrum that similar tothe frequency spectrum of the received signals (104). In this context,receiver 202/302 operates in a conventional manner. Namely, receiver202/302 demodulates fax signal 104 to extract therefrominformation/messages, in binary format. Thereafter, the fax relay statemachine forwards the extracted binary data through T.30 command/responseanalyzer 205/305 and outputs packet queue 208/308 to packetizer 110,which packetizes the binary data and forwards the resulting FoIP packets111 (FIGS. 1, 2 and 3) to the packet interface 112 (FIG. 1)

However, if the state machine of gateway 200 determines that signal 104does not relate to fax control type signals, a second decision isreached, as to whether signal 104 has to be demodulated according to adifferent demodulation scheme, or it has to be PCM encoded. The latterdecision depends on the signal type, as detailed hereinafter.

The ‘V xx’ receiver (203) is advantageously designed for demodulation ofsignals such as V.27 (DPSK, 2.4/4.8 kbps), V.29 (QAM, 7.2/9.6 kbps) andV.17/V.33 (Trellis code modulation—TCM, 7 2/9.6/12.0/14.4 kbps) used inG3 fax calls for T.30 training check TCF and images. Depending on agateway configuration and available resources for performingdemodulation, receiver 203 is either enabled or disabled. When invokedby the fax relay state machine, the receiver 203 extracts the TCF or faximage data (206), and forwards it through packet queue 208 to FoIPpacketizer (110), which packetizes the extracted data and forwards theresulting packets 111 (FIGS. 1 and 2) to the packet interface 112 (FIG.1)

The PCM encoder (204) performs G.711 A-law, or μ-law, type compressionof signals that the state machine determined that they should betransferred ‘transparently’ Theoretically, the state machine may decideto disable, or mute, V.xx demodulation activities related to any one ofthe modulation standards V.27, V 29, V.17 and V.33, in which case thedisabled Phase C fax image and preceding Phase B TCF signals would betransferred using PCM mode of operation In case of V.34 fax calls, thefollowing groups of signals are transferred as PCM encoded signals: Lineprobe (Phase B) signals, Primary channel equalizer training (Phase B)signals, and Primary channel (Phase C) signals. The fax relay 200packetizes (110) the resulting PCM data by utilizing rules that aredictated by the FoIP protocol

According to current T38 Recommendation, the V.34 INFO and line probeand V.34 equalizer training signals are not relayed but, instead, theyare locally generated in/by the gateway. Also the T.30 TCF signal may belocally generated by the gateway According to the present invention,V.34 INFO signals are relayed after being demodulated, and V.34 lineprobe, V.34 equalizer training and optionally T.30 TCF signals aretransferred by means of PCM. This is essential for effective adaptationof the fax rate involved to the current line conditions and forsuccessful reception of post-coming Phase C image signals by ananswering fax machine

The present invention makes use of the T.38 protocol version 04/2004,which is extended for the purposes of the present invention using threeT.30 INDICATORS and two T.30 DATA types The three T.30 INDICATORS are:

-   -   V.34 INFO;    -   PCM, G 711μ-law; and    -   PCM, G.711 A-law.

The two T.30 DATA types are

-   -   INFO data; and    -   PCM data.

Synchronously with processing the input fax signals, the gateways 200and 300 transmit the output signals to connected fax machines. Bydefault, in the absence of fax packets from the IP network, the faxrelay transmitter mutes its output

The fax relay de-packetizer 218/318 receives the FoIP bit stream fromthe IP network (“FoIP Packet In”), recovers lost packets, re-orderspackets arriving in incorrect sequence, and removes excess redundancydata. The resultant data is buffered according to its type (i.e.,210/310, 313 or 316). The fax relay state machine decides if, when andhow to re-modulate or decode (as the case may be) the arriving data in away to conform to the fax transmission protocol T 30.

Relayed fax control signals pass through the T.30 response/command queue210/310 and are re-modulated by transmitter 212/312. The T.30response/command signal/data generator 211/311 operates in conjunctionwith T.30 response/command queue 210/310 in order to locally generateT.30 signals/data for preventing the abortion of connections betweenrespective fax terminal equipments in cases of incoming packets beingdelayed. The duration of transmitted fax control signals is adjusted tonetwork delays by varying the length of tonal components and amount ofHDLC flags or fill bits

The fax image or TCF data relayed from an originating side passesthrough the V xx jitter buffer 313 and is re-modulated by V.xxtransmitter 315. Though this is not necessarily so, V.xx transmitter 315of the answering gateway usually re-modulates data by using a modulationstandard and a data rate similar to those used by a remote gateway andthe originating fax. The V.xx data generator 314 is utilized as a sourceof binary data for image related signals that can or should be locallygenerated by gateway 300. For example, such image related data may belocal TCF, HDLC flags and T.4 fill bits.

When FRP-PCM type stream arrives from the IP network, the data stream isfirst buffered (316) and then PCM decoded (317) to produce the outputsignal.

It is noted that fax relays 200 (FIG. 2) and 300 (FIG. 3) actually referto the same novel fax relay that is disclosed herein. FIGS. 2 and 3schematically illustrate the ‘originating’ and ‘answering’ portions,sections or elements, of the fax relay, respectively, as explicitlydescribed hereinbefore.

The method disclosed in the present invention is advantageous over theprior art in that it offers a compromise between two traditionalmethods, i.e., FoIP and VBD:

-   -   The method disclosed by the present invention is advantageous        over VBD in terms of reliability and bandwidth utilization; and    -   The gateway disclosed by the present invention has lower        complexity vs. traditional FoIP gateways, because, according to        the novel principles that are disclosed in the present        invention, signal modulation standards that are dedicated by        T.30 Recommendation for fax image transmission (V.27, V.29,        V.17/V.33, and V34) may be spared

In comparison to VBD, the method and fax relay disclosed by the presentinvention are advantageous in other aspects. For example, transferringfax control signals enjoys the benefits of FoIP vs. VBD. Morespecifically, the method and fax relay disclosed by the presentinvention are characterized by:

-   -   Saving bandwidth for fax control signals and silence periods        relayed at low bit-rates;    -   Having half-duplex PCM type data stream, thereby saving a        communication bandwidth that would otherwise be required for        backwards channeling,    -   Being free of echoes: the novel gateway never returns echoes        over IP to a remote gateway and connected fax and, therefore, it        presents a much better signal-to-noise ratio,    -   Being well protected from signal/data collisions because it        transmits the fax signals according to T.30 signal flow        definition;    -   Being well protected from packet loss for fax control signals;    -   Enabling fax spoofing for solving problems of signal delay        caused by the IP network and/or by the fax machine involved in        the fax communication;    -   Overcoming T 30 violations; and    -   Suppressing the influence of network jitters and clock        synchronization errors by means of long enough buffering of PCM        data stream that is received from the IP network.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those skilled in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

1. A method of delivering in real-time fax calls from a gateway to an IPnetwork, comprising distinguishing between a first type of signals and asecond type of signals, wherein signals belonging to said first type aretransferred by said gateway to said IP network after being demodulatedin said gateway, and signals of said second type are transferred by saidgateway to said IP network either after being demodulated or after beingPCM encoded based on a predetermined condition.
 2. A method according toclaim 1, wherein the first type of signals is generally associated with‘fax control signals’ and the second type of signals is generallyassociated with ‘fax image signals’.
 3. A method according to claim 1,wherein if the predetermined condition is met, a signal of the secondtype is relayed by the gateway after being demodulated; otherwise, saidsignal is transferred after being PCM encoded.
 4. A method according toclaim 3, wherein the predetermined condition relates to the availabilityof computational resources in the gateway that are required forperforming the demodulation process, and/or to whether the gateway bothsupports the modulation scheme used by the fax machines with which saidgateway is in communication.
 5. A method according to claim 2, whereinthe ‘fax control signal’ is any signal belonging to the group of signalsconsisting of {Answer fax tone including V.8 modified answer tone; V.21(FSK, 300 bps), V.34 INFO (DPSK, 600 bps); V.34 Control Channel (QAM,1200 bps or 2400 bps)}.
 6. A method according to claim 2, wherein the‘fax image signal’ is any signal belonging to the group of signalsconsisting of: {V.27 (Phases B and C); V 29 (Phases B and C); V.17/V.33(Phases B and C); V.34 Line probe (Phase B); V.34 Primary channelequalizer training (Phase B); V.34 Primary channel (Phase C)}.
 7. Amethod for processing in real-time an outgoing fax over IP (“FoIP”)signal by a gateway, comprising: a) receiving said fax signal and, basedon its signal characteristics, associating it either with a first typeof signals or with a second type of signals; and b) demodulating saidfax signal if it is associated with said first type of signals or if itis associated with said second type of signals and based on a predefinedcondition, and outputting the resultant FRP packetized data to the IPnetwork, or c) PCM-encoding said fax signal and outputting the resultantFRP-PCM packetized data to said IP network based on said predefinedcondition.
 8. A method according to claim 7, wherein the first type ofsignals is generally associated with ‘fax control signals’ and thesecond type of signals is generally associated with ‘fax image signals’.9. A method according to claim 7, wherein the predetermined conditionrelates to the availability of computational resources in the gatewaythat are required for performing the demodulation process, and/or towhether the gateway both supports the modulation scheme used by the faxmachines with which said gateway is in communication
 10. A methodaccording to claim 8, wherein the ‘fax control signal’ is any signalbelonging to the group consisting of: {Answer fax tone including V.8modified answer tone; V.21 (FSK, 300 bps); V.34 INFO (DPSK, 600 bps);V.34 Control Channel (QAM, 1200 bps or 2400 bps)}.
 11. A methodaccording to claim 8, wherein the ‘fax image signal’ is any signalbelonging to the group consisting of: {V.27 (Phases B and C); V.29(Phases B and C); V.17/V.33 (Phases B and C); V.34 Line probe (Phase B);V.34 Primary channel equalizer training (Phase B), V.34 Primary channel(Phase C)}
 12. A method for processing by a gateway in real-time a faxover IP (“FoIP”) signal received from an IP network, comprising: a)determining whether said received fax signal is FRP-type data or FRP-PCMtype data; b) re-modulating said fax signal if it is determined to beFRP-type data, and forwarding the resultant signal to an intendedrecipient; or c) PCM-decoding said incoming fax signal if it isdetermined to be FRP-PCM type data, and forwarding the resultant signalto said recipient.
 13. A fax relay for processing in real-time anoutgoing fax signal before delivering it to an IP network, comprising:a) an interface for interfacing with a fax terminal equipment; b)distinguishing means, for distinguishing between a first type of signalsand a second type of signals, and for associating said fax signal eitherwith said first or with said second type of signals; c) a storage meansfor storing therein a predetermined condition and for judging whethersaid condition is met; and d) demodulator and PCM encoder fordemodulating fax signals and for PCM encoding fax signals, respectively,and for outputting corresponding packets to said IP network. wherein,signals belonging to said first type are relayed by said fax relay tosaid IP network after being demodulated in said fax relay, and signalsof said second type are transferred by said fax relay to said IP networkeither after being demodulated or after being PCM encoded, based on saidpredetermined condition.
 14. A fax relay according to claim 13, whereinthe first type of signals is generally associated with ‘fax controlsignals’ and the second type of signals is generally associated with‘fax image signals’.
 15. The fax relay according to claim 13, whereinthe predetermined condition relates to the availability of computationalresources in the gateway that are required for performing thedemodulation process, and/or to whether the gateway both supports themodulation scheme used by the fax machines with which said gateway is incommunication.
 16. The fax relay according to claim 14, wherein the ‘faxcontrol signal’ is any signal belonging to the group consisting of:{Answer fax tone including V.8 modified answer tone; V.21 (FSK, 300bps); V.34 INFO (DPSK, 600 bps); V.34 Control Channel (QAM, 1200 bps or2400 bps)}.
 17. The fax relay according to claim 14, wherein the ‘faximage signal’ is any signal belonging to the group consisting of: {V.27(Phases B and C), V.29 (Phases B and C); V17/V.33 (Phases B and C); V 34Line probe (Phase B); V.34 Primary channel equalizer training (Phase B);V.34 Primary channel (Phase C)}.
 18. The fax relay according to claim13, further comprising: a receiver for receiving packets from the IPnetwork, which packets relating to received fax call signals, a bufferfor buffering said packets; a local signal/data generator for locallygenerating fax-related signals to prevent the abortion of a connectionbetween respective fax terminal equipments in cases where incomingpackets are delayed; re-modulator and PCM-decoder for re-modulatingdemodulated fax signals and for PCM-decoding PCM-encoded fax signals,respectively; and an interface for communicating with a fax terminalequipment.